much better than Safari since you can _reattach_ tabs back into the main window

Unless I am misunderstanding you, this is possible in Safari (though potentially inelegant). Tabs can be dragged to, from and between any two tabbed windows. If you have only a single document window, though (i.e. one or no tabs showing, depending on your prefs setting), you must first induce the display of a new tab before being able to drag the principal document.